blob: 1a4eee620b0d91aea2bc46a1b59484eecb572aac [file] [log] [blame]
Davide Libenzi5dc8bf82007-05-10 22:23:11 -07001/*
2 * fs/anon_inodes.c
3 *
4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
5 *
6 * Thanks to Arnd Bergmann for code review and suggestions.
7 * More changes for Thomas Gleixner suggestions.
8 *
9 */
10
11#include <linux/file.h>
12#include <linux/poll.h>
13#include <linux/slab.h>
14#include <linux/init.h>
15#include <linux/fs.h>
16#include <linux/mount.h>
17#include <linux/module.h>
18#include <linux/kernel.h>
19#include <linux/magic.h>
20#include <linux/anon_inodes.h>
21
22#include <asm/uaccess.h>
23
24static struct vfsmount *anon_inode_mnt __read_mostly;
25static struct inode *anon_inode_inode;
26static const struct file_operations anon_inode_fops;
27
28static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
29 const char *dev_name, void *data,
30 struct vfsmount *mnt)
31{
32 return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC,
33 mnt);
34}
35
36static int anon_inodefs_delete_dentry(struct dentry *dentry)
37{
38 /*
39 * We faked vfs to believe the dentry was hashed when we created it.
40 * Now we restore the flag so that dput() will work correctly.
41 */
42 dentry->d_flags |= DCACHE_UNHASHED;
43 return 1;
44}
45
46static struct file_system_type anon_inode_fs_type = {
47 .name = "anon_inodefs",
48 .get_sb = anon_inodefs_get_sb,
49 .kill_sb = kill_anon_super,
50};
51static struct dentry_operations anon_inodefs_dentry_operations = {
52 .d_delete = anon_inodefs_delete_dentry,
53};
54
55/**
J. Bruce Fields4b4e5a12007-07-15 23:41:53 -070056 * anon_inode_getfd - creates a new file instance by hooking it up to an
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070057 * anonymous inode, and a dentry that describe the "class"
58 * of the file
59 *
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070060 * @name: [in] name of the "class" of the new file
Ulrich Drepper7d9dbca2008-07-23 21:29:22 -070061 * @fops: [in] file operations for the new file
62 * @priv: [in] private data for the new file (will be file's private_data)
63 * @flags: [in] flags
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070064 *
65 * Creates a new file by hooking it on a single inode. This is useful for files
66 * that do not need to have a full-fledged inode in order to operate correctly.
J. Bruce Fields4b4e5a12007-07-15 23:41:53 -070067 * All the files created with anon_inode_getfd() will share a single inode,
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070068 * hence saving memory and avoiding code duplication for the file/inode/dentry
Al Viro2030a422008-02-23 06:46:49 -050069 * setup. Returns new descriptor or -error.
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070070 */
Al Viro2030a422008-02-23 06:46:49 -050071int anon_inode_getfd(const char *name, const struct file_operations *fops,
Ulrich Drepper7d9dbca2008-07-23 21:29:22 -070072 void *priv, int flags)
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070073{
74 struct qstr this;
75 struct dentry *dentry;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070076 struct file *file;
77 int error, fd;
78
79 if (IS_ERR(anon_inode_inode))
80 return -ENODEV;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070081
Ulrich Drepper7d9dbca2008-07-23 21:29:22 -070082 error = get_unused_fd_flags(flags);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070083 if (error < 0)
Dave Hansen430e2852008-02-15 14:37:26 -080084 return error;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070085 fd = error;
86
87 /*
88 * Link the inode to a directory entry by creating a unique name
89 * using the inode sequence number.
90 */
91 error = -ENOMEM;
92 this.name = name;
93 this.len = strlen(name);
94 this.hash = 0;
95 dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
96 if (!dentry)
97 goto err_put_unused_fd;
Davide Libenzi96fdc722007-10-16 23:30:19 -070098
99 /*
100 * We know the anon_inode inode count is always greater than zero,
101 * so we can avoid doing an igrab() and we can use an open-coded
102 * atomic_inc().
103 */
104 atomic_inc(&anon_inode_inode->i_count);
105
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700106 dentry->d_op = &anon_inodefs_dentry_operations;
107 /* Do not publish this dentry inside the global dentry hash table */
108 dentry->d_flags &= ~DCACHE_UNHASHED;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700109 d_instantiate(dentry, anon_inode_inode);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700110
Dave Hansen430e2852008-02-15 14:37:26 -0800111 error = -ENFILE;
112 file = alloc_file(anon_inode_mnt, dentry,
113 FMODE_READ | FMODE_WRITE, fops);
114 if (!file)
115 goto err_dput;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700116 file->f_mapping = anon_inode_inode->i_mapping;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700117
118 file->f_pos = 0;
119 file->f_flags = O_RDWR;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700120 file->f_version = 0;
121 file->private_data = priv;
122
123 fd_install(fd, file);
124
Al Viro2030a422008-02-23 06:46:49 -0500125 return fd;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700126
Dave Hansen430e2852008-02-15 14:37:26 -0800127err_dput:
128 dput(dentry);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700129err_put_unused_fd:
130 put_unused_fd(fd);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700131 return error;
132}
Avi Kivityd6d28162007-06-28 08:38:16 -0400133EXPORT_SYMBOL_GPL(anon_inode_getfd);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700134
135/*
J. Bruce Fields4b4e5a12007-07-15 23:41:53 -0700136 * A single inode exists for all anon_inode files. Contrary to pipes,
137 * anon_inode inodes have no associated per-instance data, so we need
138 * only allocate one of them.
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700139 */
140static struct inode *anon_inode_mkinode(void)
141{
142 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
143
144 if (!inode)
145 return ERR_PTR(-ENOMEM);
146
147 inode->i_fop = &anon_inode_fops;
148
149 /*
150 * Mark the inode dirty from the very beginning,
151 * that way it will never be moved to the dirty
152 * list because mark_inode_dirty() will think
153 * that it already _is_ on the dirty list.
154 */
155 inode->i_state = I_DIRTY;
156 inode->i_mode = S_IRUSR | S_IWUSR;
157 inode->i_uid = current->fsuid;
158 inode->i_gid = current->fsgid;
159 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
160 return inode;
161}
162
163static int __init anon_inode_init(void)
164{
165 int error;
166
167 error = register_filesystem(&anon_inode_fs_type);
168 if (error)
169 goto err_exit;
170 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
171 if (IS_ERR(anon_inode_mnt)) {
172 error = PTR_ERR(anon_inode_mnt);
173 goto err_unregister_filesystem;
174 }
175 anon_inode_inode = anon_inode_mkinode();
176 if (IS_ERR(anon_inode_inode)) {
177 error = PTR_ERR(anon_inode_inode);
178 goto err_mntput;
179 }
180
181 return 0;
182
183err_mntput:
184 mntput(anon_inode_mnt);
185err_unregister_filesystem:
186 unregister_filesystem(&anon_inode_fs_type);
187err_exit:
188 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
189}
190
191fs_initcall(anon_inode_init);
192